1. Field of the Invention
This invention relates to a work mounting apparatus which utilizes cycloid motion to receive, as works, electronic components such as ICs, capacitors and resistors, from work feeders and to mount the received works onto printed boards.
2. Description of the Related Art
This type of work mounting apparatus is disclosed, for example, in U.S. Pat. No. 5,305,518. The work mounting apparatus disclosed in this U.S. patent has head units arranged along the outer periphery of a drum, and the head units are each rotatable about a turning shaft extending in the radial direction of the drum. Each head unit includes a nozzle head and a balance weight, and the nozzle head has a suction nozzle directed downward. The work mounting apparatus further comprises a plurality of work feeders and a printed board arranged along the outer periphery of the drum, the printed board being placed on an XY table.
As the drum is rotated in one direction, each head unit also is rotated about the turning shaft thereof, causing the suction nozzle to make cycloid motion.
If the cycle of the cycloid motion is suitably controlled, the suction nozzle can attract a work thereto by suction from a desired work feeder and mount the attracted work onto the printed board, by means of the cycloid motion. The cycle of the cycloid motion is controlled by changing the rotational speed of the head unit, that is, the turning shaft thereof.
The balance weight of the head unit is useful in stabilizing the cycloid motion of the nozzle head, but it inevitably increases the mass of the head unit as a whole. Therefore, when the cycle of the cycloid motion of the nozzle head is controlled, the kinetic energy of the head unit greatly varies since the mass of the head unit is large, causing elastic, torsional deformation of the turning shaft of the head unit. Such torsional deformation of the turning shaft increases as the rotational speed of the drum, that is, the speed of the cycloid motion of the nozzle head, increases with the operational speed of the work mounting apparatus.
The elastic, torsional deformation of the turning shaft gives rise to vibration of the head unit, that is, the nozzle head, in the rotating direction of the unit. In some cases, therefore, the suction nozzle fails to securely receive and mount a work.
In order to prevent the torsional deformation of the turning shaft, the diameter of the turning shaft may be increased so that the shaft may have increased rigidity, but in this case, a disadvantage arises in that the work mounting apparatus itself is increased in size.